1. Field of the Invention
The present invention relates to a laser projector to display an image by scanning light from a laser light source to a projection screen.
2. Description of Related Art
As a laser projector using laser as a light source, there is known a laser projector which displays an image by scanning laser beam from a laser light source on a screen by an electromagnetic driven scan mirror which is made to vibrate back and forth.
The scan mirror has its innate resonance frequency which is determined by the size and the density and hardness of the material, and by driving the scan mirror at the resonance frequency, the scan mirror is made to vibrate in maximum deflection angle and a large image can be displayed at low power.
FIG. 10A shows a relation between deflection angle of a scan mirror and frequency and FIG. 10B shows a relation between deflection angle of a scan mirror and frequency under different environments. As shown in FIG. 10A, for example, there is a need to drive the scan mirror at a frequency within a range of fd2 to fd1 in order to drive the scan mirror in a deflection angle θa or above. However, individual variation in the resonance frequency of the scan mirror according to the product cannot be avoided and it is difficult to make the scan mirror vibrate in a sufficient deflection angle by driving the scan mirror at the optimum frequency from the beginning at the time of start-up of the laser projector. Particularly, the inclination is steep near the resonance point in the waveform of the frequency and the deflection angle fluctuates greatly even when the frequency shifts slightly.
Moreover, as shown in FIG. 10B, the resonance frequency of each scan mirror is greatly influenced by surrounding temperature environment and the like. Therefore, according to an environment, the scan mirror does not always vibrate in a deflection angle θa or more even when the scan mirror is driven at a frequency within a range of fd2 to fd1. Therefore, driving of the scan mirror at the time of start-up is even more difficult.
When the laser light source is emitted in a state where the deflection angle of the scan mirror is not sufficiently assured at the time of start-up, the laser beam which is reflected by the scan mirror will be emitted so as to concentrate within a narrow range. Particularly, because there is a possibility that a person may be in front of the screen at the time of start-up of the projector, there is a possibility of damaging a human body by the laser beam which has a high energy density.
Thereby, for example, JP2004-333698 discloses a projector comprising a light scan detection unit to detect whether the galvanometer mirror is carrying out the scanning operation normally or whether the galvanometer mirror is not carrying out the scanning operation normally. In such projector, a method in which the generation of laser beam can be surely blocked to improve the safety by blocking the power supply to the laser light source when it is detected by the light scan detection unit that the galvanometer mirror is not carrying out the scanning operation normally is applied.
However, JP2004-333698 is a technique to block the generation of the laser beam to the laser light source every time when it is detected that the galvanometer mirror is not carrying out the operation normally while the projector is being used, and this does not solve the problem specific to the start-up of the above described laser projector. Namely, that problem is the possibility of having high energy density light, which is due to the emitted laser beam being concentrated within a narrow range at the time of start-up of the projector due to the scan mirror not vibrating in a sufficient deflection angle, impinging upon a human body.